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CASS™ ZIP + 4® Coding

CASS™ (USPS® certification process for ZIP + 4 matching software) is a certification program used by the United States Postal Service® to ensure the quality of ZIP + 4 coding systems. Processing a mailing list through a CASS Certified ZIP + 4 system is required to receive USPS presort discounts.

To take advantage of automation discounts, the mailing list must be CASS processed within 180 days of the mail date. Carrier route discounts require the mailing list be CASS processed within 90 days of the mail date, and basic presort discounts require the mailing list be ZIP Code™ verified within one year of the mail date.

Some addresses will not be + 4 coded because they do not match the ZIP + 4 database; these are potentially problem addresses. Error codes are offered to help you understand what might be missing or incorrect with your addresses that do not + 4 code.

ZIP + 4 coding works in ranges and even though an address + 4 codes, there is no guarantee it is a known delivery point. To confirm whether or not an address is a known USPS delivery point, we provide the DPV® service as part of our ZIP + 4 processing. DPV processing also identifies whether or not an address is a commercial mail receiving agency.